What In Neptune's World: Can You Identify This Coral?

Welcome to What in Neptune's World - a new column intended to explore the wonders of the coral reefs in an entertaining, interactive manner. You're invited to discuss this column with fellow reefkeepers in Reefs.org's General Reef Discussion Forum.

This month, we have a mystery coral seeking identification. The answer will be announced the General Discussion Forum the first week of the following month. In the meanwhile, feel free to discuss the possibilities with other hobbyists.

Can you identify this coral? It has been in my reef tanks for at least 10 years. I now have it in two colonies. It is a coral that thrives in relatively low light. (click to enlarge)